Method and apparatus for guiding side edges of continuously running web

ABSTRACT

The present invention is to provide a method and an apparatus facilitating side edges of a web continuously running in a machine direction to be quickly corrected when these side edges are detected to be out of coincidence with a positions in a cross direction orthogonal to the machine direction. Roll means rotating about a shaft extending in a direction defined between a machine direction and a cross direction are put in contact with side edge of a web continuously running in the machine direction. The shaft is mounted on an arm adapted to rotate back-and-forth so that the shaft can swing in- and outward in the cross direction. Downstream of the roll means, the side edge is position-detected and the arm is made swing by a desired angle determined on the basis of a difference between the actual position and a desired position.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus allowing, inthe course of continuously feeding a flexible web of nonwoven fabric,plastic film, paper or the like in a machine direction, side-edges ofsuch a web to be guided to desired positions in a cross directionorthogonal to the machine direction.

It is well known in prior art references 1, 2, 3 listed below, in thecourse of continuously feeding a flexible web of nonwoven fabric,plastic film, paper or the like in a machine direction, to put guideroll means rotating about respective shafts each obliquely extending ata desired angle with respect to the machine direction in contact withthe vicinities of side edges of such a web and thereby to move the sideedges so that the web may be broadened. It is also well known that theweb can be unwrinkled by guiding the side edges of the web. Prior artreference discloses a method for guiding the side edges of the webcontinuously fed to desired positions by operatively associating suchguide roll means with detector means adapted to detect actual positionsof the web.

Prior art reference 1: GB Patent Publication No. 1,373,682

Prior art reference 2: U.S. Pat. Publication No. 4,920,622

Prior art reference 3: U.S. Pat. Publication No. 2,718,046

Of the apparatuses disclosed in Prior art references 1 through 3, oneapparatus has the guide roll means fixed at a predetermined anglerelative to the machine direction, another apparatus is adapted to varya contact pressure between the guide roll means and the web, and furtheranother apparatus has the guide roll means in the form of paired niprolls adapted to vary a nip pressure against the web. When it isintended to guide the side edges of the web detected to be out of.coincidence with desired positions to these desired positions byappropriately varying the contact pressure or the nip pressure, it isrelatively easy to shift the side edges outward in the axial directionof the guide roll means, i.e., outward in the cross directioncorresponding to the transverse direction of the web. However, it isdifficult to shift the side edges in the directions other than theoutward direction, for example, inward in the cross direction. For theseapparatuses disclosed in Prior art references 1, 2, 3 respectivelyprovided with such guide roll means, it has been impossible to guide theside edges of the web little by little with a high accuracy or toposition-shift the side edges of the web quickly. In addition, the webof nonwoven fabric, plastic film or the like which has been tightlywounded around a roll core generally exhibits a subtle variation in awidth of the web as the web is released and fed in the machine directiondirectly from such tightly wound state. Such subtle variation of thewidth of the web may occur also due to a pulling force exerted on theweb in the machine direction. Synergistic effect of these variationdestabilizes the width of the web and therefore destabilizes positionsof the side edges of the web in the cross direction. In consequence, itis difficult to continuously make articles each having a highdimensional accuracy by utilizing the side edges of the web.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method and anapparatus facilitating the side edges of the web continuously running inthe machine direction to be quickly guided to desired positions in thecross direction when these side edges are detected to be out ofcoincidence with the desired positions in the cross direction.

According to a first aspect of the present invention, there is provideda method for guiding a web continuously running in a machine directionand having a pair of side edges opposed to each other in a crossdirection orthogonal to the machine direction so that at least one ofthe side edges is guided to a predetermined position in the crossdirection by putting roll means rotating about a shaft extending in adirection defined between the machine direction and the cross directionin contact with a vicinity of at least one of the side edges.

The first aspect of the present invention comprises the steps of:mounting an arm having a proximal end and a distal end opposed to theproximal end at the proximal end on a pivot pin adapted to rotateback-and-forth so that the arm swings about the pivot pin in- andoutward as viewed in the cross direction, supporting the shaft of theroll means by the distal end of the arm so that the roll means alsoswing about the pivot pin in- and outward, detecting, at downstream ofthe roll means, a position of the one side edge immediately after thisside edge has been guided, and driving the arm by driving means adaptedto operate on the basis of a difference between the position detected inthis manner and the predetermined position so that the arm swings in- oroutward in the cross direction by a predetermined angle.

The present invention on the first aspect may be implemented also inmanners as follow:

The driving means comprises an extensible/retractable arm operativelyassociated with a servomotor adapted to rotate in a direction and at arotational frequency depending on the difference between the detectedposition and the predetermined position and thereby to extend or retractthe extensible/retractable arm so that the side edge is guided to thepredetermined position.

The roll means is put in contact with at least one side of the web.

The roll means comprises a pair of rolls extending in parallel to eachother and adapted to nip at least one side edge and a vicinity thereof.

The roll means are provided in vicinities of a pair of the side edges toguide these side edges to the respective predetermined positions.

According to a second aspect of the present invention, there is providedan apparatus for guiding a web continuously running in a machinedirection and having a pair of side edges opposed to each other in across direction orthogonal to the machine direction so that at least oneof the side edges is guided to a predetermined position in the crossdirection by putting roll means rotating about a shaft extending in adirection defined between the machine direction and the cross directionin contact with a vicinity of at least one of the side edges.

The second aspect of the present invention further comprising thefollowing features: The shaft of the roll means is supported on a distalend of an arm having a proximal end and the distal end opposed to theproximal end; the proximal end of the arm is mounted on a pivot pinadapted to rotate back-and-forth so that the arm swings about the pivotpin in- and outward as viewed in the cross direction; detector means isprovided downstream of the roll means in the machine direction to detecta position of the one side edge after this side edge has been guided;and the arm is operatively associated with driving means adapted tooperate on the basis of a difference between the position detected bythe detector means and the predetermined position so that the arm swingsin- or outward in the cross direction by a predetermined angle.

The second aspect of the present invention may be implemented also inmanners as follow:

The driving means comprises an extensible/retractable arm operativelyassociated with a servomotor.

The roll means is put in contact with at least one side of the web.

The roll means comprises a pair of rolls extending in parallel to eachother and adapted to nip at least one side edge and a vicinity thereof.

The roll means are provided in vicinities of a pair of the side edges toguide these side edges to the respective desired positions.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view showing a partially cutaway disposable diaper;

FIG. 2 is a diagram illustrating a part of process for making thedisposable diaper;

FIG. 3 is a diagram illustrating a part of FIG. 2 in an enlarged scale;

FIG. 4 is a sectional view taken along the line IV-IV in FIG. 3;

FIG. 5 is a sectional view taken along the line V-V in FIG. 3;

FIG. 6 is a diagram illustrating a part of FIG. 5 in an enlarged scale;

FIG. 7 is a sectional view taken along the line VII-VII in FIG. 5;

FIG. 8 is a sectional view taken along the line VIII-VIII in FIG. 5;

FIG. 9 is a view similar to FIG. 3, illustrating one preferredembodiment of the present invention; and

FIG. 10 is a view similar to FIG. 4, illustrating this embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Details of a method and an apparatus according to the present inventionwill be more fully understood from the description given hereunder withreference to the accompanying drawings.

A disposable diaper 1 shown by FIG. 1 in a plan view as partially brokenaway is a product obtained by a method and an apparatus according to thepresent invention. This diaper 1 comprises a liquid-pervious topsheet 2,a liquid-impervious backsheet 3 and a liquid-absorbent core 4 interposedbetween these sheets 2, 3. The diaper 1 has a in- and outward direction(longitudinal direction as viewed in FIG. 1) and a waist-surroundingdirection (transverse direction as viewed in FIG. 1). The diaper 1 isperipherally contoured by a pair of side edges 11 extending parallel toeach other in the in- and outward direction and a pair of ends extendingparallel to each other in the waist-surrounding direction. As viewed inthe in- and and outward direction, the diaper 1 is composed of a frontwaist region 6, a rear waist region 7 and a crotch region 8 extendingbetween these waist regions 6, 7 wherein tape fasteners 13 laterallyextend from the side edges 11 in the rear waist region 7. The topsheet 2may be formed from liquid-pervious materials such as nonwoven fabrics oraperture plastic films, the backsheet 3 may be formed fromliquid-impervious materials selected from plastic films, nonwovenfabrics and plastic film/nonwoven fabric laminates. The diaper 1 furthercomprises elastic members attached in a stretched state thereto so as toextend along the side edges 11 and the ends 12.

FIG. 2 is a plan view illustrating a part of process for continuouslymaking the diaper 1, FIG. 3 is a scale-enlarged plan view illustrating apart of FIG. 2 and FIG. 4 is a partially cutaway sectional view takenalong the line IV-IV in FIG. 3. As viewed in FIG. 2, a first continuousweb 21 destined to form the backsheet 3 of the diaper 1 is continuouslyfed in a machine direction MD downward from above. The continuous web 21is guided through an edge controller 40 to control a width of the web 21to a desired dimension and then loaded thereon with the cores 4 whichare arranged intermittently in the machine direction MD. Then, secondcontinuous web 22 destined to form the topsheet 2 of the diaper 1 iscontinuously fed so as to cover the cores 4 whereupon the firstcontinuous web 21 and the second continuous web 22 are joined togetheraround the respective cores 4 by means of adhesives or a suitablewelding technique to form a continuous assembly 26. The continuousassembly 26 is cut along lines each extending in a cross direction CDorthogonal to the machine direction MD between each pair of the adjacentcores 4 followed by attaching a pair of the tape fasteners 13 to thefirst web 21 of each unit assembly cut from the continuous assembly 26.In this manner, the individual diapers 1 as shown by FIG. 1 areobtained. In FIGS. 2, 3 and 4, the first and second continuous webs 21,22 as well as the cores 4 are indicated by imaginary lines and, in FIG.2, the diaper 1 is illustrated as partially broken away.

The first continuous web 21 has first and second side edges 31, 32opposed to each other in the cross direction CD and extending parallelto each other in the machine direction MD. The edge controller 40functions as a controlling means for the first continuous web 21.Specifically, the edge controller 40 guides at least one of vicinitiesof the first side edge 31 and the second side edge 32 to a positionpredetermined position in the cross direction CD and thereby controlsthe width of the first continuous web 21 to a desired dimension. Theedge controller 40 exemplarily illustrated comprises a first edgecontroller 41 operatively associated with the first side edge 31 and asecond edge controller 42 operatively associated with the second sideedge 32. These two edge controllers 41, 42 are substantially identicalto each other, so the first edge controller 41 will be primarilydescribed with reference to FIGS. 2 through 4. The term used herein“vicinities of the respective side edges” should be understood toinclude the respective side edges and the vicinities thereof.

The first edge controller 41 includes a movable plate 47 adapted to bemovable in the cross direction CD relative to a base plate 46 extendingacross the first continuous web 21. The movable plate 47 is providedwith an actuator 48 and a swing arm 49. A support bar 51 mounted on thebase plate 46 downstream in the machine direction MD and extending inthe cross direction CD is provided with a photoelectric sensor unit 52.The photoelectric sensor unit 52 electrically connected with theactuator 48 functions to detect an actual position of the first sideedge of the first continuous web 21 and to compare this actual positionto a predetermined position on which the first side edge 31 should fall.Based on such comparison, the photoelectric sensor unit 52 calculates adirection and a distance in and by which the first side edge 31 shouldbe shifted to the predetermined position. The actuator 48 comprising aservomotor 53, a extensible/retractable arm 54 and a ball screw joint(not shown) interposed between these motor 53 and the arm 54 rotates themotor 53 in accordance with the direction and the distance calculated bythe photoelectric sensor unit 52 and thereby and thereby extends orretracts the arm 54 depending on a result of calculation. A distal endof the extensible/retractable arm 54 is rotatably connected to a distalend 59 of the swing arm 49 by means of a pivot pin 56. A proximal end 57of the swing arm 49 opposite to the distal end 59 is mounted on themovable plate 47 by means of a pivot pin 58 around which the swing arm49 can swing in- and outward in the cross direction CD. The distal end59 of the swing arm 49 is provided with a roll unit 63 specificallycomprising first and second nip rolls 61, 62 arranged vertically asviewed in FIG. 4. The roll unit 63 comprises a bracket 64 fixed to theswing arm 49, a supporter 67 extending from this bracket 64 and supportsa first rotary shaft 66 at its opposite ends and a second rotary shaft68 extending from the bracket 64 and supports the second nip roll 62 atits opposite ends. The first nip roll 61 and the second nip roll 62 arefree to rotate about the first rotary shaft 66 and the second rotaryshaft 68, respectively, both in the machine direction MD and in thedirection opposite to the machine direction MD.

The photoelectric sensor unit 52 shown in FIG. 4 has an upper arm 82provided with a light emitter 82 a extending in the cross section CD anda lower arm 83 provided with a light receiver 83 a extending in thecross section CD. From the light receiver 83 a, an output cord 83 bextends toward the actuator 48. The unit 52 is adapted to detect thefirst side edge 31 of the first continuous web 21 indicated by imaginaryline. In FIGS. 2 and 3, a photoelectric sensor unit 152 in the secondedge controller 42 of the edge controller 40 is shown as mounted on asupport bar 151, but this photoelectric sensor unit 152 is not shown inFIG. 4.

With the edge controller 40 constructed in this manner, an actualposition of the first side edge 31 detected by the photoelectric sensorunit 52 located downstream of the first edge controller 41 is comparedwith the predetermined position on which the first side edge 31 shouldfall. Operation of the actuator 48 based on such comparison causes theswing arm 49 connected with the extensible/retractable arm 54 to swingabout the pivot pin 58 by a desired angle inward or outward in the crossdirection CD, i.e., inward or outward in the transverse direction of thefirst continuous web 21. The roll unit 63 mounted on the distal end 59of the swing arm 49 also swings as the swing arm 49 swings in thismanner.

In the roll unit 63, the first rotary shaft 66 of the first nip roll 61and the second rotary shaft 68 of the second nip roll 62 extend betweenthe machine direction MD and the cross direction CD and normally extendso as to intersect the machine direction MD. In FIGS. 2 and 3, the firstnip roll 61 extending in the transverse direction of the firstcontinuous web 21 after having slightly swung from the cross directionCD toward the machine direction MD is indicated by solid line while thefirst nip roll 61 having significantly swung outward in the transversedirection of the first continuous web 21 is indicated by imaginary line.The second nip roll 62 underlies the first nip roll 61 and therefore cannot be seen in FIGS. 2 and 3. The roll unit 63 functions to move thefirst side edge 31 and its vicinity of the first continuous web 21nipped between the first and second nip rolls 61, 62 outward in thetransverse direction as the swing arm 49 swings outward in thetransverse direction of the first continuous web 21. In this course, thefirst and second nip rolls 61, 62 substantially falling on the crossdirection as viewed in FIGS. 2 and 3 swing so that their respectiveinner ends 61 a, 62 a put aside inward in the transverse direction ofthe first continuous web 21 move to downstream of their respective outerends 61 b, 62 b put aside outward in the transverse direction of thefirst continuous web 21 as viewed in the machine direction MD. In otherwords, swing of the arm 49 outward in the transverse direction of thefirst continuous web 21 causes the rotary shafts 66, 68 of the first andsecond nip rolls 61, 62 to swing so that a tilt angle a of these rotaryshafts 66, 68 relative to the machine direction MD gradually decreases.The movable plate 47 on which the first edge controller 41 is mounted isfixed at a position in the cross direction CD adjusted so that the firstand second nip rolls 61, 62 can repetitively swing at any given time inthe vicinity of the first side edge 31 of the first continuous web 21.

Similar to the first edge controller 41, the second edge controller 42constituting the edge controller 40 comprises a movable plate 147mounted on the base plate 46 so that its position in the cross directionCD may be adjusted, an actuator 148, a swing arm 149, a pivot pin 148, aroll unit 163 and a photoelectric sensor unit 152. Of these referencenumerals, those added with 100 designate the components constituting thesecond edge controller 42. In the second edge controller 42, the rollunit 163 is placed in a mirror symmetric relationship with the roll unit63 in the first edge controller 41 and the other components such as theactuator 148 and the swing arm 149 are mounted on the movable plate 147in an appropriate layout allowing such mirror symmetric relationshipbetween these roll units 63. 163. The arm 149 adapted to in- and outwardswing on the basis of data supplied from the photoelectric sensor unit152 adapted to detect an actual position of the second side edge 32. Inresponse to swing of this arm 149 outward in the transverse direction ofthe first continuous web 21, the first and second nip rolls 161, 162 ofthe roll unit 163 swing in the same manner as in the case of the firstand second nip rolls 61, 62 of the roll unit 63 so that so that theirrespective inner ends 161 a, 162 a put aside inward in the transversedirection of the first continuous web 21 move to downstream of theirrespective outer ends 161 b, 162 b put aside outward in the transversedirection of the first continuous web 21 as viewed in the machinedirection MD with a tilt angle β of these nip rolls 161 b, 162 brelative to the machine direction MD gradually decreasing. The first andsecond edge controllers 41, 42 operate independently of each other.

FIG. 5 is a sectional view taken along the line V-V in FIG. 3, showingprofiles of the second edge controller 42 and the photoelectric sensorunit 152. In FIG. 5, the roll unit 163 is oriented in coincidence withthe cross direction CD. In the second edge controller 42, the pivot pin158 of the swing arm 149 lies upstream in the machine direction MD androtatably mounted on a pedestal 171 which is, in turn, fixed to themovable plate 147. The swing arm 149 extends from upstream towarddownstream in the machine direction MD and provided on its distal end159 with the roll unit 163 fixed thereto. In the vicinity of the distalend 159, the extensible/retractable arm 154 is mounted on the swing arm149 by means of the pivot pin 156 so that the arm 154 can rotate aroundthe pivot pin 156. The roll unit 163 comprises the first nip roll 161and the second nip roll 162. After having been nipped by these two rolls161, 162, the first continuous web 21 horizontally runs through thephotoelectric sensor unit 152 and further runs toward downstream in themachine direction MD as indicated by imaginary line.

FIG. 6 is a scale-enlarged view showing the roll unit 163 FIG. 5, FIG. 7is a sectional view taken along the line VII-VII, and FIG. 8 is asectional view taken along the line VIII-VIII in FIG. 5, respectively.The roll unit 163 has a bracket 164 fixed to the swing arm 149. Thebracket 164 has inner and outer surfaces 173, 174 placed aside inwardand outward, respectively as viewed in the transverse direction of thefirst continuous web 21. From the inner surface 173, a cylindrical arm176 horizontally extends and supports the first nip roll 161 and thisarm 176 is provided on its inner end 176 a with an inverted. squareU-shaped supporter 167 mounted thereon by means of coupling means 177 aswill be seen in FIG. 8. The supporter 167 rotatably supports oppositeends of a first rotary shaft 166 of the first nip roll 161. Also fromthe inner surface 173, a second rotary shaft 168 supporting the secondnip roll 162 horizontally extends and rotatably mounted on the bracket164. From the outer surface 174 of the bracket 164, an outer end 176 bof the cylindrical arm 176 extends and a plate member 179 is fixedaround this outer end 176 b. One end of a coil spring 181 operativelyassociated with the nip roll unit is anchored on the plate member 179and the opposite end of the coil spring 181 is anchored on an angularplate 172 a of the bracket 164.

In the roll unit 163 constructed in this manner, the bracket 164 swingsin- and outward integrally with the swing arm 149 around the pivot pin158. The first nip roll 161 is rotatable about the first rotary shaft166 toward down- and upstream in the machine direction MD. Thecylindrical arm 176 is supported by the bracket 164 and rotatable in twodirections indicated by a double-headed arrow A (See FIG. 6). While thefirst nip roll 161 can be brought in contact with or spaced from thesecond nip roll 162 as the cylindrical arm 176 rotates, the first niproll 161 is normally biased by the spring 181 to come in contact withthe second nip roll 162. The first nip roll 161 is also rotatable aroundthe coupling means 177 in the direction indicated by the double-headedarrow B (See FIG. 8). The second nip roll 162 is supported by thebracket 164 by means of the second rotary shaft 168 and rotatable towarddownstream as well as toward upstream in the machine direction MD. Swingof the first nip roll 161 in the directions indicated by thedouble-headed arrows A and B causes the vicinity of the second side edge32 of the first continuous web 21 nipped between the first nip roll 161and the second nip roll 162 to be held in close contact with these tworolls 161, 162 and thereby to follow in- and outward swinging of thesetwo rolls 161, 162.

The first and second nip rolls 61, 62 of the roll unit 63 and the firstand second nip rolls 161, 162 of the roll unit 163 tilt at angles of αand β relative to the machine direction MD when the roll units 63, 163respectively nip the vicinity of the first side edge 31 and the vicinityof the second side edge 32 of the first continuous web 21. Consequently,a force tending to broaden a transverse dimension of the firstcontinuous web 21 is exerted on the extent of this web 21 between thefirst and second side edges 31, 32 thereof. If the first continuous web21 guided through the edge controller 40 has wrinkles, the force tendingto broaden the web 21 functions to unwrinkled the web 21. When sucheffect is not required, the roll units 63, 163 may be previously swungin the respective directions in which the tilt angles α and β areappropriately decreased. The directions in which the pair of the firstand second nip rolls 61, 62 and the pair of the first and second niprolls 161, 162 are swung about the pivot pins 58, 158, respectively maybe appropriately selected to move the vicinity of the first side edge 31and the vicinity of the second side edge 32 nipped by these pairs of thenip rolls, respectively, together with these rolls outward as well asinward in the transverse direction of the first continuous web 21.

As will be understood from the aforementioned description, the methodand the apparatus according to the present invention is primarily inthat a swinging direction and a swinging extent (i.e., swinging angle)of the first and second nip roll pairs 61, 62; 161, 162 are linked withthe respective positions of the first and second side edges 31, 32 ofthe first continuous web 21 detected by the photoelectric sensor units52, 152, respectively. More specifically, the photoelectric sensor units52, 152 are provided immediately downstream of the respective roll units63, 163 so that a combined effect of the first and second nip roll pairs61, 161; 161, 162 swinging in this direction and by this extent may berapidly fed back to the respective actuators 48, 148 and thereby thefirst continuous web 21 may be rapidly and accurately controlled. It isalso possible to ensure a rapid position-change of the first and secondside edges 31, 32 by accelerating the servomotors rotational velocitiesand thereby accelerating the swinging velocities of the roll units 63,163.

FIG. 9 is a view similar to FIG. 3, showing one preferred embodiment ofthe present invention and FIG. 10 is a view similar to FIG. 4, showingthis embodiment. The edge controller 40 according to this embodiment isdistinguished from that shown by FIGS. 2 through 4 in that each of thefirst and second edge controllers 41, 42 comprises a lower roll 262, 362adapted to come in contact with the lower surface of the firstcontinuous web 21 and not an upper roll adapted to come in contact withthe upper surface of the first continuous web 21. While the positions atwhich the lower rolls 262, 362 are provided are substantially the sameas those at which the second nip rolls 62, 162 of FIG. 4 are provided,the first edge controller 41 according to the embodiment shown by FIGS.9 and 10 is distinguished from the previous embodiment shown by FIG. 4in that a bracket 264 is mounted on a swing arm 249 so that the bracket264 may swing about the arm 249. The lower roll 262 mounted on thebracket 264 extends inward in the transverse direction of the firstcontinuous web 21 so as to describe a rising slope (See FIG. 10) as thebracket 264 appropriately swings. This is true for the lower roll 362 ofthe second edge controller 42. The first continuous web 21 is broughtinto a state as shown by FIG. 10 as these lower rolls 262, 362 arepressed against the vicinities of the first and second side edges 31,32, respectively. Then, these rolls 262, 362 in- and outward swingtogether with the respective swing arms 249, 349 in the transversedirection of the first continuous web 21 and thereby guide the first andsecond side edges 31, 32 to the desired positions. According to thisembodiment also, the positions actually the first and second side edges31, 32 passing after having been guided by the rolls 262, 362 aredetected by photoelectric sensor units 252, 352 and actuators 248, 348operate in response to data supplied from these sensor units 252, 352 sothat the side edges 31, 32 may be guided to the predetermined positionsmore accurately. Slopes at which the lower rolls 262, 362 should tiltmay be appropriately adjusted taking account of particularcharacteristics of the first continuous web 31 such as flexibility,elasticity and slipperiness.

While the invention has been described hereinabove on the basis of theembodiments in which the first and second side edges 31, 32 includingthe vicinities thereof of the first continuous web 21 are guided by thefirst and second end controllers 41, 42, respectively, to the desiredpositions, the invention may be implemented in a manner that only one ofthe side edges including the vicinity of this side edge is guided to thedesired position. Without departing from the scope of the invention, analternative arrangement is also possible in which the first and secondnip rolls 61, 62 are shifted from each other in the machine directionMD, i.e., one of the nip rolls is located upstream and the other islocated downstream in the machine direction MD. Factors such asmaterial, type of surface finish, length and diameter may beappropriately selected depending on the manner in which the firstcontinuous web 21 has been processed and coated with adhesive, if any.The roll may be formed from use of materials, for example, sponge rubberobtained from various types of rubber such as urethane rubber andsilicone rubber or metallic material. The roll may be subjected to asurface treatment such as a satin-like finish to adjust a slipperinessrelative to the first continuous web 21. Means for position-detection ofthe first and second side edges 31, 32 is not limited to thephotoelectric sensor unit as illustrated and this photoelectric sensorunit may be replaced by the other optical means or physical means. Whilethe present invention has been described with respect to the firstcontinuous web 21 used for the disposable diaper 1, the invention isapplicable also to the second continuous web 22 and the other types ofcontinuous web used for articles other than the diaper 1.

According to the present invention, the rotatable rolls used to come incontact with the vicinities of the side edges of the web continuouslyrunning in the machine direction and thereby to guide these side edgesin the cross direction are adapted to swing in- and outward in thetransverse direction of the web wherein the direction and the extend(angle) of swing relative to the machine direction are determined on thebasis of the detected positions of the respective side edges of therunning web. According to the present invention, the angle of the rollsrelative to the machine direction can be adjustably varied to vary aforce tending to broaden the web and at the same time the positions ofthe side edges of the web can be forcibly and quickly varied byoscillating the rolls. In this way, the side edges of the web can beeasily and accurately guided to the predetermined position.

1. A method for guiding a web continuously running in a machinedirection and having a pair of side edges opposed to each other in across direction orthogonal to said machine direction so that at leastone of said side edges is guided to a predetermined position in saidcross direction by putting roll means rotating about a shaft extendingin a direction defined between said machine direction and said crossdirection in contact with a vicinity of at least one of said side edges,said method comprising the steps of: mounting an arm having a proximalend and a distal end opposed to said proximal end at said proximal endon a pivot pin adapted to rotate back-and-forth so that said arm swingsaround said pivot pin in- and outward as viewed in said cross direction;supporting said shaft of said roll means by said distal end of said armso that said roll means also swing about said pivot pin in- and outward;detecting, at downstream of said roll means, a position of said one sideedge after this side edge has been guided; and driving said arm bydriving means adapted to operate on the basis of a difference betweensaid position detected in this manner and said desired position so thatsaid arm swings in- or outward in said cross direction by apredetermined angle.
 2. The method according to claim 1, wherein saiddriving means comprises an extensible/retractable arm operativelyassociated with a servomotor adapted to rotate in a direction and at arotational frequency depending on the difference between said detectedposition and said desired position and thereby to extend or retract saidextensible/retractable arm so that said side edge is guided to saiddesired position.
 3. The method according to claim 1, wherein said rollmeans is put in contact with at least one side of said web.
 4. Themethod according to claim 1, wherein said roll means comprises a pair ofrolls extending in parallel to each other and adapted to nip at leastsaid one side edge and the vicinity thereof.
 5. The method according toclaim 1, wherein said roll means are provided in vicinities of a pair ofsaid side edges to guide these side edges to respective said desiredpositions.
 6. An apparatus for guiding a web continuously running in amachine direction and having a pair of side edges opposed to each otherin a cross direction orthogonal to said machine direction so that atleast one of said side edges is guided to a predetermined position insaid cross direction by putting roll means rotating about a shaftextending in a direction defined between said machine direction and saidcross direction in contact with a vicinity of at least one of said sideedges, said apparatus further comprising: said shaft of said roll meansbeing supported on a distal end of an arm which has a proximal end andsaid distal end opposed to said proximal end; said proximal end of saidarm being mounted on a pivot pin adapted to rotate back-and-forth sothat said arm swings about said pivot pin in- and outward as viewed insaid cross direction; detector means being provided downstream of saidroll means in said machine direction to detect a position of said oneside edge immediately after said one side edge has been guided; and saidarm being operatively associated with driving means adapted to operateon the basis of a difference between said position detected by saiddetector means and said desired position so that said arm swing in- oroutward in said cross direction by a desired angle.
 7. The apparatusaccording to claim 6, wherein said driving means comprises anextensible/retractable arm operatively associated with a servomotor. 8.The apparatus according to claim 6, wherein said roll means is put incontact with at least one side of said web.
 9. The apparatus accordingto claim 6, wherein said roll means comprises a pair of rolls extendingparallel to each other and adapted to nip at least said one side edgeand the vicinity thereof.
 10. The apparatus according to claim 6,wherein said roll means are provided in vicinities of a pair of saidside edges to guide these side edges to respective said predeterminedpositions.